1. Field of the Invention
The present invention relates to a disk storage device such as a magnetic disk device or an optical disk device, and more particularly to means for calculating a compensation signal for cancelling an external disturbance which acts on a head positioning control system, storing it, and supplying it to a drive circuit as a part of input signals to suppress the external disturbance, improve a head positioning precision and shorten a head positioning time.
2. Related Background Art
In many of the prior art magnetic disk devices, a system for floating a magnetic head as a rotation speed of the disk increases has been adopted, and it is necessary to position the head externally of a data area when the device is started and stopped in order to protect the data storage area. Usually, an actuator is pushed in one direction by a spring called a retract spring or the head is retracted externally of the data area by the weight of the actuator. The spring force and the weight of the actuator are causes of the external disturbance and the effect on the head positioning control system is significant and it causes a variation in the transitional response by an error in a steady state position or a difference in a direction of movement.
The disk storage device, is vibrated according to a rotating frequency since the disk is rotated at a high rotation speed, and this vibration acts on the position signal as the external disturbance and deteriorates the positioning precision.
Where a velocity control system is used as a control system for moving the head to a target track and a velocity detector estimates a velocity signal based on the position signal and a drive signal, the external disturbance of the disk vibration causes a detection error and a variation in the response of the velocity control system.
Further, in the prior art optical disk device, in order to position the head, a coarse actuator for driving a large distance and a fine actuator for finely positioning after the drive by the coarse actuator are provided, and the head is mounted on the fine actuator. For the fine positioning, it is necessary that the fine actuator be activated, but when the eccentricity of the disk is large compared to a stroke of the fine actuator, the positioning by the fine actuator is not attained and the positioning precision is lowered.
As an external disturbance compensation method, JP-A-1-43378 proposes a compensation method in which an error signal of an estimated velocity signal and a velocity signal is fed back to be added to an input of a power amplifier as an external disturbance cancellation signal.
As the speed and the capacity of the disk storage device increase, spacing between tracks has been reduced more and more and the weight of an actuator has been greatly reduced. As a result, the affect of the external disturbance is more and more discernable. In the disk storage device, when a center of rotation of the disk does not coincide with a center of gravity, the disk is vibrated at the rotating frequency. Accordingly, it is important to suppress the external disturbance. There is a limit from a resonance characteristic of a head support mechanism in suppressing the external disturbance.
In the prior art method for estimating and suppressing the external disturbance it disclosed in JP-A-1-43378, the error between the detected velocity signal and the estimated velocity signal is amplified and fed back. It can suppress a low frequency external disturbance but when a high frequency mechanical vibration is to be suppressed, a signal derived by differentiating the position signal including a high frequency noise as a velocity signal, a S/N ratio of the velocity signal is lowered and a frequency band of a position differentiation circuit cannot be set high. As a result, the high frequency external disturbance and vibration cannot be suppressed. In a method of feeding back an estimated error, a delay by the feedback compensation is included and good compensation of the external disturbance is not attained.